scheduling tasks to execute PHP files related issues

scheduling tasks to execute PHP file issues
Wrote a a.php file,
And wrote a bat, the content is:
C:\wamp\bin\php\php5.3.8\php.exe-f E:\photoselect\work\a.php

Execute bat regularly in Task Scheduler, set 5 minutes to execute once

But often 5 minutes is not finished, will be 5 minutes later ran a bat, this will be wrong,
(In the scheduled task has been set to the time is not run to complete, not a new instance), but seemingly invalid, do not know if this is not only for EXE

Thank you for your help.

------Solution--------------------
5 minutes to deal with, can only find ways to improve the efficiency of a.php, check the bottleneck where, consider multithreading.


In addition to not complete the new instance, is for bat, PHP you need to implement the duplicate process detection.
------Solution--------------------
Modify the a.php file when running to determine whether there is still running, is the word to exit directly. No words. Run end Destroy flag

